Abstract

The activity and catalytic properties of two preparations of acid phosphatases from potato and sweet potato in the presence of different levels of manganese (Mn) and molybdenum (Mo) were determined. Preliminarily, two different methods usually suggested in literature for the assay of acid phosphatase activity were compared. Since the methodology using acetate buffer gave a higher transformation of the substrate, it was selected for investigating the effect of the metals on the enzymes. The two plant acid phosphatases showed significant differences in their catalytic properties and behaviour in response to the presence of Mn and Mo. Sweet potato acid phosphatase displayed higher activity levels and a greater substrate affinity than potato enzyme. Furthermore, a significant decrease of Vmax and a small increment of Km values were measured in the presence of 0.58 and 1.17 mM of Mn ions. No significant effects were observed for the potato enzyme. The two enzymes showed the greater difference in their activity and kinetic behaviour when evaluating the effect of increasing levels of Mo (0.001 to 0.01 mM). Both the enzymes were competitively inhibited by the anion but with a different intensity at all Mo levels. The different number of protein subunits and purity levels of the two enzymes as ascertained by electrophoretic studies may account for the observed differences. © 2007 Taylor & Francis.